In a known electronic device having an imaging function, such as a digital still camera and a digital video camera, a solid-state imaging element such as a charge coupled device (CCD) and a complementary metal oxide semiconductor (CMOS) image sensor is employed, for example. The solid-state imaging element includes a pixel combining a photodiode (PD) that performs photoelectric conversion and a plurality of transistors. An image is constructed on the basis of a pixel signal output from a plurality of the pixels arranged on an image plane on which an image of a subject is formed.
Furthermore, in order to accommodate the pixels in a pixel region with limited area, it is necessary to form the pixel with as few transistors as possible, and a source follower amplifier is adopted as an amplification transistor in typical cases. Since the source follower amplifier can arrange a constant current source outside the pixel region, it is possible to reduce the area of the pixel region, and possible to drive a large capacitive load by amplifying the current. On the other hand, since the source follower amplifier has a voltage amplification factor of 1 or less, it is disadvantageous compared with a voltage amplification type amplifier in terms of a signal/noise (SN) ratio against noise in a subsequent circuit.
Accordingly, in order to suppress the occurrence of noise, the applicant of the present invention has proposed a solid-state imaging element having a portion of a gate electrode constituting an amplification transistor with a protrusion buried in a substrate on which a PD is formed (for example, refer to Patent Document 1).